IP-TCP_METRICS(8)         (23 Aug 2012)         IP-TCP_METRICS(8)

     NAME
          ip-tcp_metrics - management for TCP Metrics

     SYNOPSIS
          ip [ OPTIONS ] tcp_metrics { COMMAND | help }

          ip tcp_metrics { show | flush } SELECTOR

          ip tcp_metrics delete [ address ] ADDRESS

          SELECTOR :=  [ [ address ] PREFIX ]

     DESCRIPTION
          ip tcp_metrics is used to manipulate entries in the kernel
          that keep TCP information for IPv4 and IPv6 destinations.
          The entries are created when TCP sockets want to share
          information for destinations and are stored in a cache keyed
          by the destination address. The saved information may
          include values for metrics (initially obtained from routes),
          recent TSVAL for TIME-WAIT recycling purposes, state for the
          Fast Open feature, etc.  For performance reasons the cache
          can not grow above configured limit and the older entries
          are replaced with fresh information, sometimes reclaimed and
          used for new destinations. The kernel never removes entries,
          they can be flushed only with this tool.

        ip tcp_metrics show - show cached
          address PREFIX (default)
               IPv4/IPv6 prefix or address. If no prefix is provided
               all entries are shown.

          The output may contain the following information:

          age <S.MMM>sec - time after the entry was created, reset or
          updated with metrics from sockets. The entry is reset and
          refreshed on use with metrics from route if the metrics are
          not updated in last hour. Not all cached values reset the
          age on update.

          cwnd <N> - CWND metric value

          fo_cookie <HEX-STRING> - Cookie value received in SYN-ACK to
          be used by Fast Open for next SYNs

          fo_mss <N> - MSS value received in SYN-ACK to be used by
          Fast Open for next SYNs

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          fo_syn_drops <N>/<S.MMM>sec ago - Number of drops of initial
          outgoing Fast Open SYNs with data detected by monitoring the
          received SYN-ACK after SYN retransmission.  The seconds show
          the time after last SYN drop and together with the drop
          count can be used to disable Fast Open for some time.

          reordering <N> - Reordering metric value

          rtt <N>us - RTT metric value

          rttvar <N>us - RTTVAR metric value

          ssthresh <SSTHRESH> - SSTHRESH metric value

          tw_ts <TSVAL>/<SEC>sec ago - recent TSVAL and the seconds
          after saving it into TIME-WAIT socket

        ip tcp_metrics delete - delete single
          address ADDRESS (default)
               IPv4/IPv6 address. The address is a required argument.

        ip tcp_metrics flush - flush entries
          This command flushes the entries selected by some criteria.

          This command has the same arguments as show.

     EXAMPLES
          ip tcp_metrics show address 192.168.0.0/24
              Shows the entries for destinations from subnet

          ip tcp_metrics show 192.168.0.0/24
              The same but address keyword is optional

          ip tcp_metrics
              Show all is the default action

          ip tcp_metrics delete 192.168.0.1
              Removes the entry for 192.168.0.1 from cache.

          ip tcp_metrics flush 192.168.0.0/24
              Removes entries for destinations from subnet

          ip tcp_metrics flush all
              Removes all entries from cache

          ip -6 tcp_metrics flush all
              Removes all IPv6 entries from cache keeping the IPv4
              entries.

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     SEE ALSO
          ip(8)

     AUTHOR
          Original Manpage by Julian Anastasov <ja@ssi.bg>

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